1. Field of the Invention
This invention relates to a matrix switching apparatus for selectively outputting information signals supplied to a plurality of input terminals at desired output terminals. More particularly, it relates to a matrix switching apparatus made up of a plurality of switching units each including a plurality of input terminals and a plurality of output terminals.
2. Description of Related Art
In broadcasting stations or production studios producing television broadcast programs or video recordings, video and audio signals inputted to and outputted from a plurality of pieces of equipment such as VTRs, video disk recording/reproducing apparatus, audio tape recorders, disk recording and/or reproducing apparatus, microphones or television cameras, need to be switchingly selected in a desired manner for transmission. For example, a matrix switching apparatus, comprising a matrix array of a large number of switches, is provided between a plurality of editing rooms and a VTR chamber in which a large number of VTRs and a variety of recording/reproducing apparatus are densely installed so that on optionally selecting and controlling desired switches of the matrix switching apparatus, a desired piece of equipment or one not in use may be designated for use by a given editing room from a large number of pieces of equipment in the VTR chamber.
For such a matrix switching apparatus, the required matrix size varies depending on the overall system size and may be determined by, for example, the number of pieces of equipment to be in use or the number of editing rooms. There are cases wherein a large system with tens of input and output channels is required. It is, however, difficult for a single matrix switching apparatus to meet these varying requirements. For this reason, it has been proposed to construct a large matrix switching apparatus by using a plurality of small to medium size matrix switching units each comprising several to tens of channels, as proposed in U.S. patent application No. 07/674,890 previously filed in the name of the present Assignee.
FIG. 1 shows an example of a matrix switching apparatus made up of a plurality, herein four, of the above mentioned matrix switching units MSU to enhance the number of input and output terminals.
Each of the four matrix switching units MSU.sub.1 to MSU.sub.4 shown in FIG. 1 has 32 channels input terminals TI.sub.1 to TI.sub.32 and 32 channel output terminals TO.sub.1 to TO.sub.32 and switches arranged at crosspoints or points of intersection between extension lines of these input terminals TI.sub.1 to TI.sub.32 and extension lines of the output terminals TO.sub.1 to TO.sub.32 for providing a 32 x 32 switch matrix. Each of the matrix switching units MSU.sub.1 to MSU.sub.4 has 32 channel extension output terminals EO.sub.1 to EO.sub.32 and 32 channel extension input terminals EI.sub.1 to EI.sub.32. Using these four matrix switching units MSU.sub.1 to MSU.sub.4, the extension input terminals EI.sub.1 to EI.sub.32 of the matrix switching unit MSU.sub.1 are connected to the output terminals TO.sub.1 to TO.sub.32 of the matrix switching unit MSU.sub.2, the extension output terminals EO.sub.1 to EO.sub.32 of the matrix switching unit MSU.sub.1 are connected to the input terminals TI.sub.1 to TI.sub.32 of the matrix switching unit MSU.sub.4, the extension output terminals EO.sub.1 to EO.sub.32 of the matrix switching unit MSU.sub.2 are connected to the input terminals TI.sub.1 to TO.sub.32 of the matrix switching unit MSU.sub.3 and the extension output terminals TO.sub.1 to TO.sub.32 of the matrix switching unit MSU.sub.3 are connected to the input terminals TI.sub.1 to TI.sub.32 of the matrix switching unit MSU.sub.4 for providing a matrix switching apparatus having 64 channel input x 64 channel outputs. In this case, it suffices if 32 of the 64 channel inputs, namely the inputs IN.sub.1 to IN.sub.32, are supplied respectively to the input terminals TI.sub.1 to TI.sub.32 of the matrix switching unit MSU.sub.1 and the remaining 32 channel inputs IN.sub.33 to IN.sub.64 are supplied respectively to the input terminals TI.sub.1 to TI.sub.32 of the matrix switching unit MSU.sub.2, while 32 of the 64 outputs, namely the outputs OUT.sub.1 to OUT.sub.32, are taken out at the respective output terminals TO.sub.1 to TO.sub.32 of the matrix switching unit MSU.sub.1 and the remaining 32 channel outputs OUT.sub.33 to OUT.sub.64 are taken out at the output terminals TO.sub.1 to TO.sub.32 of the matrix switcher unit MSU.sub.4. It becomes possible in this manner to distribute the 64 channel inputs IN.sub.1 to IN.sub.64 so as to be taken out as 64 channel outputs OUT.sub.1 to OUT.sub.64.
In a conventional switching matrix apparatus, a remote control unit is provided for making or breaking respective crosspoint switches, and desired input and output signal routing (route switching) may be realized by actuating buttons or changeover levers on a control panel of the remote control unit. In a matrix switching apparatus having a plurality of matrix switching units, a plurality of the above mentioned remote control units are occasionally provided, in which case it becomes necessary to provide a signal configuration, that is a protocol or format, for exchanging control signals or the like between the matrix switching units and the remote control units.
Moreover, if several to less than twenty pieces of equipment are to be used, only one serial busline suffices for exchanging the control signals or the like. However, if signal transmission is to be made over a serial busline between tens to hundreds of pieces of equipment, response time or reliability may be lowered and an excessive waiting time may occur before actual signal route switching is achieved, or a special cable may need to be used because of an increased data error rate. If different communication functions of the units need to be provided, it is necessary to provide units performing these different communication functions by a painstaking and laborious operation.
Further, if the above described matrix switching apparatus is connected to, for example, an apparatus that receives digital signals, such as serial digital video signals, since the switching apparatus usually regenerates the input digital signals, it becomes necessary to change the clock frequency depending on the format of the input digital signals The clock signals are generated by a voltage-controlled oscillator (VCO) or the like. Supposing that a similar regenerating circuit is provided for waveforming at the output of each crosspoint switch of the matrix switcher apparatus, signals can not properly be outputted if the clock frequency at the input side differs from that at the output side.
Also in the above described matrix switching apparatus or a matrix switching apparatus composed of a plurality of matrix switching units, inspection of the switching states, that is, checking whether the switching operation of a large number of switches provided in a matrix configuration is performed properly is usually accomplished by monitoring output signals from the respective channels. For this reason, a signal is not outputted or transmitted due to defective switching operations of one of the switches of the matrix switching apparatus, which of the switches is out of order can be determined only by an extremely time-and labor-consuming operation.
It is noted that, in a system comprising interconnection of the above described conventional matrix switching apparatus and remote control units, failure to make a response to transmitted data within a predetermined time is considered to be a sign of the occurrence of a malfunction such as busline breakage or shorting of the transmission line. However, it is not possible with the conventional system to determine if the malfunction is ascribable to shorting or to breakage.